Such apparatus is generally based on the rolling principle, one on the other, of two superimposed cutting cylinders, with parallel axes, one of them being engraved in raised relief and the other one being smooth. In some processes however, the two cylinders can carry complementary engraving. The driving in rotation of the cylinders, at the same peripheral speed but in a reverse direction to one another, is provided by connection gears having the same pitch diameter chosen so that there remains, between the two cutting cylinders, a short and constant distance necessary for ensuring a good cut of the cardboard or paper web passing therebetween, without nevertheless any contact between the rotary parts performing the cut.
The gap separating the two cutting cylinders of parallel axes is provided by rolling rollers which are fixed to the ends of the two cylinders while being perfectly concentrical therewith. The diameter of each of these rolling rollers is equal to the pitch diameter of the connection gear. Thus, the cutting pressure can be applied without restriction on the two cylinders.
The diameter of the cutting cylinders which depends of the cut out format has also to be determined, as a function of the web width, in such manner that the deflections applied during the cutting operation, added to the execution tolerances, are not superior than to the theoretical distance separating the cutting parts. The deflections which appear during the cutting operation have two origins, viz. the deflection as such of the cylinders under the effect of a load which is punctual or uniformly distributed, due to the cutting effort, and the deflection caused by the sagging moments due the effort exerted on the cylinder spindles. The first deflection can be attenuated only by increasing the diameter of the cutting cylinders. The second deflection can be totally eliminated by applying the cutting pressure directly on the rolling rollers. This pressure is generally applied by means of two shafts of large diameter, with axes parallel to the axes of the cutting cylinder and placed respectively above and below these two cylinders. These shafts, the rotation of which can be free, are made interdependent with rolling rollers which are mounted in opposition with respect to the rolling rollers of the cutting cylinders and which roll on the latter. The pressure necessary for the cutting operation is then applied on the spindles of the two shafts, and this pressure is transmitted to the cutting cylinders via the rolling rollers in contact with one another, therefore without passing via the spindles of the cutting cylinders, thereby avoiding the deformation which would otherwise occur.
Such a known cutting apparatus has obviously the disadvantage to have a particularly complex and costly structure. Another disadvantage of this known cutting apparatus is associated with the format changing operation. Actually, when there is such an operation, it is necessary to preserve a same level to the plane of the cardboard or paper web to be cut so as not to render the subsequent operations complex to accomplish. Therefore, for each change of format, one has to be sure that the meshing of the connecting gears, whose position varies, with the control gear is correct. This meshing can be obtained by means of a swivel arm which has to be offset and then set back when there is a change of format. In order to facilitate this operation, the swivel arm can be provided with a pneumatic jack and the gears with rolling rollers.
With a view of reducing the adjustment idle times, all these considerations lead to provide, for each new format, a complete interchangeable cutting device or "cassette" including, in addition to the cylinders for format cutting, all the other elements necessary for the cutting operation. In other words, for each change of format, the cutting device as such which corresponds to the preceding format is replaced by a new cutting device corresponding to the new format, with the control alone remaining on the machine bed. This operation entails heavy and complex handlings and increases highly the cost of the format toolings.
The object of the present invention is to remedy these disadvantages.